I just acquired a really nice Gewehr 88, made in Berlin in 1890.
The owner, a friend of mine, has been shooting Remington 8mm in it for 40 years.
I am thinking of going milder, with some cast bullets and 13 grains of Red Dot.

Any shooters of old Mausers out there?

You have a "Commisssion Rifle". Cast bullets are an excellent idea because it likely has the original .318 bore. The M98's after 1905 had a .323 bore and the cartridge was designated as "7.92x57IS or JS". The older guns were "S". US ammo has been downloaded from the start because it could be depended upon that someone here would fire improper ammo. Slug the bore. Use cast bullets. Have fun.